Phosphors have been utilized for vacuum fluorescent displays (VFD), field emission displays (FED), plasma display panels (PDP), cathode ray tubes (CRT), white light emitting diodes (LED), and the like. In all these usages, it is required to supply an energy to an applicable phosphor to thereby excite it so as to cause it to emit light, and the phosphor is excited by an excitation source having a higher energy such as vacuum ultraviolet light, ultraviolet light, electron beam, blue light, or the like, such that the phosphor is caused to emit visible light.
However, since phosphors are exposed to the aforementioned excitation sources to resultingly cause a problem of deteriorated luminance, thereby necessitating a phosphor which is free of luminance deterioration. As such, there have been proposed a sialon phosphor, an oxynitride phosphor, and a nitride phosphor as phosphors each exhibiting less luminance deterioration, instead of the conventional silicate phosphor, phosphate phosphor, aluminate phosphor, sulfide phosphor, and the like.
One example of the sialon phosphor is produced by a production process as generally described below. Firstly, there are mutually mixed silicon nitride (Si3N4), aluminum nitride (AlN), and europium oxide (Eu2O3) at a predetermined molar ratio, followed by holding for 1 hour at a temperature of 1,700° C. in nitrogen at 1 atm (0.1 MPa), and firing by hot pressing for production (see patent-related reference 1, for example). It has been reported that α-sialon obtained by the process and activated by Eu ion is established into a phosphor which is excited by blue light at 450 to 500 nm and caused to emit yellow light at 550 to 600 nm. There has been further known a phosphor provided by adding a rare earth element to β-sialon (see patent-related reference 2), and it is shown therein that phosphors activated with Tb, Yb, and Ag are established into ones each emitting green light from 525 nm to 545 nm. Moreover, there has been known a green-aimed phosphor provided by activating β-sialon with Eu2+ (see patent-related reference 3).
Examples of oxinitride phosphors include ones each having a JEM phase or La3Si8N11O4 phase as a host material. Namely, there have been known a blue-aimed phosphor including, as a host crystal, a JEM phase (LaAl(Si6-zAlz)N10-zOz) activated with Ce (see patent-related reference 4), and a blue-aimed phosphor including, as a host crystal, La3Si8N11O4 activated with Ce (see patent-related reference 5).
Known as one example of nitride phosphors is a red-aimed phosphor including, as a host crystal, CaAlSiN3 activated with Eu (see patent-related reference 6). Further, it is reported in a patent-unrelated reference 1 that there has been obtained an orange-aimed phosphor or red-aimed phosphor having an emission peak between 580 nm and 640 nm as a phosphor including AlN as a host crystal, by synthesizing an amorphous ceramic thin-film of AlN:Eu3+ by a magnetron sputtering method at a room temperature. It is further reported in a patent-unrelated reference 2 that a phosphor obtained by activating an amorphous AlN thin-film with Tb3+ emits green light having a peak at 543 nm by electron beam excitation. Moreover, there has been reported a phosphor including an AlN thin-film activated with Gd3+ in a patent-unrelated reference 3. However, all the phosphors based on AlN are amorphous thin-films, and are thus unsuitable for usage in a white LED, display, and the like.
Referenced Literature/Publication:
Patent-related reference 1: JP-A-2002-363554
Patent-related reference 2: JP-A-60-206889
Patent-related reference 3: Publication matured from Japanese Patent Application No. 2004-070894
Patent-related reference 4: Publication matured from Japanese Patent Application No. 2003-208409
Patent-related reference 5: Publication matured from Japanese Patent Application No. 2003-346013
Patent-related reference 6: Publication matured from Japanese Patent Application No. 2004-41503
Patent-unrelated reference 1: Meghan L. Caldwell, et al, MRS Internet Journal Nitride Semiconductor Research, vol. 6, No. 13, p. 1-8 (2001)
Patent-unrelated reference 2: H. H. Richardson, et al, Applied Physics Letters, vol. 80, No. 12, p. 2207-2209 (2002)
Patent-unrelated reference 3: U. Vetter, et al, Physics Letters, vol. 83, No. 11, p. 2145-2147 (2003)
However, there have been demanded phosphors aimed at various colors and having higher luminances with excellent durability, for usage in white LED, plasma display, and the like each having an ultraviolet LED as an excitation source. Although the phosphors including a JEM phase and La3Si8N11O4 as host materials, respectively, have been reported as nitride phosphors or oxynitride phosphors emitting blue light, luminance thereof is not regarded as being sufficient, thereby demanding a phosphor for exhibiting a higher luminance.